Our laboratory is isolating and characterizing the proteins of the oncogenic viruses polyoma and SV40 and their temperature-sensitive mutants ts3 and ts101. We have used a two-dimensional protein separation in polyacrylamide gels, using isoelectric focusing in the first dimension and SDS-polyacrylamide gradient slab gel electrophoresis in the second dimension. We have also examined some of the major proteins by two-dimensional peptide mapping, and hope that these methods will identify the growth regulatory protein present in these viruses. We have preliminary evidence that the mutant protein of ts3 is one of the components of VP2.